1. Field of the Invention
The present invention relates to small capacitor motors including synchronous and asynchronous machines.
2. Description of the Prior Art
Generally, with respect to machines and equipment used in the fields of electrical communications, business, instrumentation, etc., many efforts are going into making a whole machine or equipment smaller, lighter, and less power consuming through the improvement of its parts with respect to materials and structures used, and hence also for electric motors used for such machines and equipment, similar requirements are naturally applied. Prior art small a.c. motors which have been used in the above described applications are shaped-pole and capacitor motors having a shaft output below about 20 watts. In particular, capacitor motors are used more frequently than shaded-pole motors when both compactness and large output are required, because the capacitor motor can be easily made to have a shaft output larger than that of the shaded-pole motor. Even for the capacitor motor, however, there is a limit in reducing size; particularly, for the prior art structure the reduction of the motor thickness in the direction of the axis of rotation has been limited. For example, FIGS. 1 and 2 of the accompanying drawings are a partially sectional front view and a partially sectional side view generally showing an example of a prior art capacitor motor, wherein a motor 1 of this type has a stator core 2 formed by, laminating in general a number of punched silicon steel plates, a stator coil 3 wound on the core 2, and a rotor 4 disposed within the hollow part of the stator. To keep the amount of magnetic flux required for the gap portion in such a motor, the thickness of the stator core 2 in the axial direction must be at least the same order as that of the rotor core 4. For this purpose, heretofore, silicon steel plates, as best shown in FIG. 2, have been laminated to the thickness equal to that of the rotor core 4A to form the stator core 2, which accepts stator coil 3. To provide desired flux, if the diameter of magnet wire is 0.09 .phi. to 0.5 .phi. mm, a coil per pole must be wound 1800 to 400 turns. Therefore, it has been said that, in prior art motors, the thickness of the stator portion in the axial direction inevitably increases by the amount occupied by the stator coil relative to the motor's thickness required in the axial direction, so that there was a limit to further reduction in the thickness of the whole motor. However, as a whole, machines and equipment are being made smaller, recently, requirements have been for smaller and thinner motors.
Considering the above described situtation, it is an object to provide a small capacitor motor reduced in thickness, as well as size, and further having high performance, such as a large shaft output.